Over the last few weeks this has come up a number of times in discussions with a couple of mastering engineers. Yes, they do matter. Do I know why? In some cases, yes. In other cases, no but I have some theories. All I know is that they do have audible effects (although not always but I’ll get to that later).
The first aspect which most people discuss is jitter. If a cable rounds off the edges of the signal in a digital cable during transmission, this can lead to increased jitter. The device on the receiving end may “trigger” a change of state at incorrect times because of the sloping on the square wave. Some devices are more influenced by this than others. Such devices are the ones which are also greatly affected by differences in clocking. A system which is not prone to jitter will not care about this rounding off of edges caused by the cable. One solution to this is to run a separate wordclock cable. The wordclock cable will affect the jitter but the other cable will be used purely as data transmission so the quality of the cable should be irrelevant. In practice, I’ve found this to not be the case and I can only theorize as to why.
My only explanation to cables which are purely for data transmission and not clocking (this includes USB cables) causing a difference has to do with noise. I believe that the electrical connection between devices can result in noise being introduced into the receiving device. Not only can this affect jitter, but it can affect any other circuitry. Paul McGowan of PS Audio once mentioned a story about their DACs sounding different when playing WAV vs FLAC files. The data was identical. They eventually found the difference to be caused by the processor in the unit using more power for decoding FLAC files which put a strain on the power supply and made other parts of the circuity behave differently. It’s not that far of a leap to think that a digital input can wreak similar havoc in a device. Is more shielding on the cable always better? No. There’s something else going on here as well. Adding to the idea of the electrical connection causing trouble, I think that grounding is also involved in this jumble of electricity.
One easy fix to this problem is to use optical cables which galvanically isolate the circuits. Unfortunately, optical cables have increased jitter so it brings us back to square one. When clocking devices with wordclock, then optical provides the perfect solution truly making the quality of the data transmission cables irrelevant. Of course then you need to worry about the quality of your wordclock cables.
What do I think is the ideal setup with digital connections? Using optical cable on a system that uses reclocking or is largely immune to jitter. The DEQX is such a device. It conveniently has all digital input formats so I’ve been able to try them all and determined this to be ideal. Upgrading to glass cables rather than plastic did offer a small improvement so it’s not completely immune to jitter. If your system is highly influenced by clocking and jitter then I recommend trying out as many formats as you can to see what works best.
It’s worth pointing out that there are some cases where the quality of the cables are irrelevant. Jitter and noise only matter in systems that involve a conversion to analog. That means any sort of recording or monitoring. In a purely digital system, then it doesn’t matter. If you have a piece of outboard with digital I/O and all you’re doing is printing something through it, then it won’t matter. The data recorded will always be identical as it’s merely a data transfer. If, however, you’re monitoring while recording through that, the quality of the cables will affect how things sound and very likely the “live” version heard while printing through it will sound different from playing back the recorded file afterwards due to differences in jitter and everything else mentioned.
Based on what I’ve said, it’s easy to see where clocking matters and doesn’t as well as why clocking matters. I won’t go in depth here but in most cases it can make large differences depending on the gear and 10MHz clocking is not the way to go. If you’re in the market for a clock, I’d recommend the Black Lion unit and the ones from Grimm Audio. For an excellent article on all things relating to clocking, check out “The Future of Clocks” on Pink Noise Magazine. A must read for all engineers in the digital era.
Shameless plug - For optical cables I’ve been using Lifatec which aren’t too expensive but are glass. For all other digital cables, I haven’t found anything that sounds better than the cables I make. If you’re interested in trying some out, get in touch with me.